A need exists in the medical field for a positioning arm for holding and stabilizing devices used in medical procedures. For example, in the field of breast biopsy, a biopsy power driver and probe, such as that disclosed in U.S. Pat. No. 5,526,822, commonly assigned with the present application, is known for percutaneously obtaining tissue samples for analysis. However, to successfully perform the procedure, it is necessary to stabilize and restrain the power driver and probe to ensure accurate placement of the probe into the breast from any desired entry point. Furthermore, once the probe has been properly positioned within the patient at the lesion site, its position must e closely maintained for an extended period of time during the tissue sampling process. Presently, either the physician or an assistant to the physician performing the procedure often undertakes this function, but fatigue often results, leading to unintended movement of the probe. As a result, numerous attempts to accurately position the probe are often necessary. In a worst case, if the unintended movements due to human error are not detected by the practitioner, the location biopsied may not be the one desired.